Dump truck pneumatically cushioned hydraulic hoist



March 1956 w, D. HOCKENSMITH, JR 2,733,773

DUMP TRUCK PNEUMATICALLY CUSHIONED HYDRAULIC I-IOIST Fi led Dec. 13. 1954 IN VEN TOR. (25250 D. HOCKENSMIT/yj, J/e.

m M 5 fr 1 Z 0 a n o 6 nited. Sees I 2,738,575 I i DUMP TRUCK. P EUMATICALLY CUSHIONED HYDRAULIIGHOIST Wilbur D. Hoc k e ni I Application Decernberxl 1954, SerialNoc474t6d6' scla stoil1121;2utj

This invention relatesto hydraulic hoists for dump ti'llCks' Hydraulic hoists of telescopic design are eomrnonly used for tilting dump truck bodies to discharge their contents. As such a' body is'raised its conte'nts'slide out, thereby progressively reducing Jthe weight'that the hoist must lift. Hence the force required to raise the loaded body initially is much greater than that required .near the The result is that the excessive shock on the hoist when it reaches the .end of its stroke sometimes drives the plunger completely out of the cylinder, thereby destroying the hoist. The relief valve may be no help because it must not operate until the maximum working pressure in the hoist is exceeded, and that does not occur normally until after the hoist is fully extended.

2,738,773 I Patented Mar. 20, 1956 lug 6pivot-a1ly mounted in the'truck frame. The hoist extends up into a recess 7 in the front end of the body and has its upper end provided with a perforated lug 8 that is pivotally connected. to the body at the top of the recess. The lower end, of -the hoist is connected by flexible inlet and outlet hoses 9 and 10,with the usual hydraulic pump (not shown) for delivering operating liquid (hydraulic fluid) to the hoist to cause it to lift the front end of the truck body to dump the, body.

' Asshown in Fig. 2, the hoist includes a telescoping cylinder 12 and plunger 13. The cylinder has a closed bottom and an open top, while the plunger has an open bottom and a closed top. The plunger may be slidably mountedin the cylinder directly if only a short hoist is I needed, but if a longer hoist is required, a sleeve 14 is slidably mounted in the cylinder and slidably receives 'the plunger. More than one telescoping sleeve may be used if a still longer hoist is needed. The lower ends of the sleeve and plunger illustrated are enlarged and will engage stop rings 16 and 17 rigidly mounted in the upper 1 ends of the cylinder and sleeve, respectively, when the hoist is fully extended. This engagement prevents the three cylindrical members 'from separating and it determines the length of thestroke of the hoist. The hoist construction described thus far .is conventional and wellknown. II t It is a feature-of this invention that as the hoist is extended to full length an internal cushion or shock absorber .will ,prevent the enlarged lower end of the plunger from striking the stop ring 17 in the upper end of; the sleeve so hard as to cause any damage or to drive theplunger out of the sleeve. Accordingly, provision is, made for an air chamber in the upper end of the It is among the objects of this invention to provide a dump truck hydraulic hoist, in which there is a selfcontained shock absorber that is eflicient, inexpensive, dependable, simple in construction and free of moving parts. r

In accordance With this invention, a substantially upright cylinder, having a closed bottom and an open top, has a hollow plunger telescoped in it. The plunger has an open bottom and a closed top. The top of the plunger is provided with a normally closed air vent. A tube com- I municates with the lower end of the vent andextends a short distance down into the plunger. With such an arrangement, when the plunger is vented before use toallow the operating liquid to fill it, a body of air will remain in the upper portion of the plunger above the lower end of the tube. This body of air forms a shock absorbing cushion when the hoist reaches full extension in use. p

The invention is illustrated in the accompanying drawings, in which: a I

Fig. 1 is a fragmentary'side view of a dump truck utilizing the hydraulic hoist;

Fig. 2 is an enlarged side view of the hoist, "with half of it shown in section; and p r Fig. 3 is a side view of the hoist fullyextended, with the upper part of the plunger shown in section.

Referring to Fig. 1 of the drawings, a dump truck body 1 is shown supportedby the frame 2 of a truck,

which in this specification means either a trailer or a plunger, wherein the air will be compressed by the hy draulic fluid when the hoist'reaches the end or" its stroke and before the fluid flow is shut oil or the usual relief valve in the system opens. The air chamber is formed by securing the upper end of a tube 20 to the lower end of the passage 21 which forms an air vent through the top of the plunger for bleeding the hoist when it is first put into use. The upper end of the vent can be provided w'itha plug or a manually operated valve 22 screwed into the side of upper lug 8. The tube extends down into the plunger a short distance, preferably about one-quarter or one-third of the way down to provide an I air'chamber of suificient capacity. Also it is desirable that the lower end of the tube be located at or near the the axis of the hoist.

axis of the plunger. One Way of doing this when the 'vent is off center is to incline the tube from the vent to By having thelower end of the tube at the center of the plunger there is no danger of bleeding too much or too little air from the hoist in case the hoist is installed or bled in a more inclined position than shown in Fig. 1.

After the hoist has been installed, hydraulic fluid is delivered to the bottom of it and vent valve 22 is opened to permit air to escape sothat the hoist can be filled with the liquid. However, as soon as the liquid reaches the lower end of tube 20, it will start to rise in the tube and the air in the plunger above the lower end of the tube will be trapped and unable to escape. As soon as hydraulic fluid starts to flow through the valve it is closed,

but the plunger will contain an air chamber having a height about equal to the length of the tube. V

Thereafter, whenever the hoist is used, the hydraulic fluid entering the bottom of the cylinder will compress the air cushion in the plunger to the pressure required to lift the load. The truck body then will start to tilt, and as the load slides out the pressure required to lift the body will decrease and the air cushion will expand.

the plunger stops moving, the hydraulic pressure will increase suddenly before the relief valve can open. Here-.

tofore, this sudden increase. in pressure put a great and dangerous strain on the hoist, but with this invention the shock is absorbed by compression of the air cushionlin the plunger, as indicated in Fig. 3.

It will be observed that my shock absorbing air cushion is formed automatically when the hydraulic system is bled of air. It does not depend upon the operator. Also, my shock absorber requires no moving parts and no attention. There is nothing to wear out or to get out ol order. The only expense is fastening the tube inside of the plunger when the hoist is made.

According to the provisions of the patent statutes, I have explained the principle of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire tohavc it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described;

I claim:

1. A telescoping hydraulic hoist for a dump truck, comprising a substantialy upright cylinder having a closed bottom and an open top and an inlet for operating liquid under pressure, a hollow plunger telescoped in the cylinder and having an open bottom and a closed top, the top of the plunger being provided with a normally closed air vent, and a tube communicating with the lower end of said vent and extending a short distance down into the plunger, whereby when the plunger is vented before use to allow the operating liquid to fill it a body of air willremain in.the upper portion of the plunger above the lower end of said tube in order to form a shock absorbing cushion when the hoist reaches full extension muse.

2. A hoist in accordance with claim 1, in which said tube extends between a quarter and a third of the Way down into said plunger. v

3. A telescoping hydraulic hoist for a dump truck, comprising a substantially upright cylinder having a closed bottom and an open top and an inlet for operating liquid under pressure, a hollow'plunger telescoped in the cylinder and having an open bottom and a closed top, the top of the plunger being provided with a normally closed air vent, and a tube having one end secured to the top of the plunger around the-lower end of said vent, the tube extending a short distance down into the plunger and having its lower end near the axis of the plunger, whereby when the plunger is vented before use to allow operating liquid to fill it a body of air will remain in the upper portion of the plunger above the lower end of said tube in order to form a shock absorbing cushion when the hoist reaches full extension in use.

Ballert Aug. 17, 1926 Barrett Feb. 11, 1941 

